1. Field of the Invention
The present invention relates to a transfer technique for transferring a toner image formed on an image bearing member onto a recording material using an electrophotographic technique used in a copying machine or a laser beam printer.
2. Description of the Related Art
Conventionally, an image forming apparatus has been used which includes a transfer portion in which a toner image formed on an image bearing member such as a photosensitive drum is transferred onto an intermediate transfer belt in an endless belt shape stretched by a plurality of rollers and then the toner image formed on the intermediate transfer belt is transferred onto a recording material. The transfer portion further includes the following configuration. A separation roller provided on an inner side of the intermediate transfer belt and a transfer counter roller provided on the inner side of the intermediate transfer belt and located on the more upstream than the separation roller in a rotation direction of the intermediate transfer belt are provided on an inside of a transfer belt. Further, a transfer roller is provided which contacts an outside surface of the intermediate transfer belt and presses the separation roller and the transfer counter roller via the intermediate transfer belt. The transfer portion includes an area in which the transfer roller contacts the intermediate transfer belt.
According to the above described configuration, a width of the transfer portion can be increased to allow suppressing an applied voltage and improving an image quality.
Japanese Patent Application Laid-Open No. 2004-029054 discusses a configuration in which an outer diameter of a separation roller is made smaller than that of a transfer roller to improve separation. In the configuration, the separation roller has the same diameter as a transfer counter roller.
If the transfer counter roller has the same outer diameter as the transfer roller or the transfer counter roller is smaller in an outer diameter than the transfer roller, the following problem occurs.
If the transfer counter roller has the same outer diameter as the transfer roller or the transfer counter roller is smaller in the outer diameter than the transfer roller, a gap between the transfer counter roller in front of the transfer portion and a recording material is widened because of curvature. If the gap between the transfer counter roller in front of the transfer portion and the recording material is wide, behavior of a rear end of the recording material being a free end may cause an electrical discharge phenomenon at the gap between the transfer counter roller and the recording material. The electrical discharge phenomenon may affect a toner image on the intermediate transfer belt.